Government evaporative emissions regulations require that engines be configured to prevent blow-by gasses, fumes, vapors, and other potential air pollutants in the engine crankcase from being released to the atmosphere. To comply with these regulations, engines typically provide some form of positive crankcase ventilation (PCV) system.
In addition to being potential atmospheric pollutants, Nitrous Oxide (NOx) in blow-by gasses also degrades oil in the crankcase, resulting in shorter usable life of the oil. This accelerated degradation of the oil can reduce engine durability, and negatively impacts the environment by requiring that the oil be changed, and hopefully recycled, more often than would be the case if the level of NOx could be reduced. It is desirable, in fact, to provide more crankcase ventilation than is required for meeting government evaporative emissions regulations, in order to promote longer oil and engine life. As will be understood from the discussion below, existing PCV systems are often incapable of providing as much crankcase ventilation as is desired.
In a typical PCV system, engine vacuum in the intake manifold is utilized for drawing a flow of air through the crankcase, to entrain blow-by gasses, fumes, vapors, and other potential air pollutants in the engine crankcase in the flow of air through the crankcase. The air with entrained potential pollutants from the crankcase is then directed by the PCV system into engine air intake, to be re-burned during the combustion process in the engine.
As is well known in the art, engine vacuum is generated in a typical engine as a result of the position of a throttle plate in a throttle body or carburetor, and varies in an inverse relationship to the power output of the engine. The power produced is a function of both the torque that the engine is producing and the speed at which the engine is running. At any time that the engine is producing output power, the highest engine vacuum occurs when the engine is operating at an idle condition, with the throttle plate nearly closed, and with the engine running essentially unloaded. Even higher engine vacuums can occur when the throttle plate is at its lowest opening, and the engine is being motored by an inertia load, and receiving rather than producing power. This condition occurs during operations such as engine braking in a vehicle. The lowest engine vacuum occurs when the engine is operating at a wide-open throttle (WOT) condition and producing maximum power. Between idle and WOT, the engine vacuum drops as a function of how widely the throttle has been opened.
The inverse relationship between available engine vacuum and engine output power creates two inherent problems that are difficult to effectively overcome in the design of a positive crankcase ventilation system utilizing engine vacuum to provide a flow of air through the crankcase.
The first problem is that when the engine is operating unloaded, at idle, with the throttle nearly closed, the available engine vacuum is so large that an excessive volume of air may be drawn through the crankcase, and introduced to the intake manifold. The amount of air from the crankcase must be kept at a small enough percentage of the air entering the engine, so that the air from the crankcase with its entrained contaminants will not adversely affect the air/fuel ratio being supplied to the engine.
The second problem is that when the engine is operating at a maximum output power condition, with the throttle at or near WOT, there is not enough engine vacuum available to draw a large enough flow of air through the crankcase to provide effective crankcase ventilation.
In order to address these problems, a PCV system utilizing engine vacuum typically includes a PCV valve, located between the crankcase and the engine air intake, for controlling the flow of air that can be drawn through the crankcase by the engine vacuum. A typical PCV valve includes a spring-loaded poppet that is positioned within a flow-controlling bore of the PCV valve by the engine vacuum.
When the engine is idling, and engine vacuum is high, the PCV valve poppet is pulled toward the engine by the high vacuum, to a position in the PCV valve bore where the flow of air from the crankcase is restricted, to keep the flow of air from the crankcase at a low enough volume that the air-fuel mixture being supplied to the engine will not be significantly diluted. When the engine is operating at an intermediate level of output power, the throttle will be opened wider, and the engine vacuum will be weaker than it is at idle. This weaker engine vacuum allows the spring in the PCV valve to move the poppet to a position in the PCV valve bore where the engine vacuum can draw an increased flow of air through the crankcase via the PCV system to remove fumes from the crankcase.
As the throttle is opened further toward WOT, so that the engine can produce more output power, the engine vacuum continues to drop, and the spring in the PCV valve moves the poppet of the PCV valve to a wide-open position where the full engine vacuum available is applied to the crankcase by the PCV system. It is difficult, however, to design a PCV valve that will function effectively in controlling the flow of air through the crankcase at all engine operating conditions, due to the inverse nature relationship of available engine vacuum with respect to output power.
As will be understood from the preceding discussion, a PCV system using engine vacuum and a traditional PCV valve may provide inefficient and ineffective removal of blow-by gasses, fumes, vapors, and other potential air pollutants from the engine crankcase.
What is needed is an improved apparatus and method for providing positive crankcase ventilation for an engine, in a manner that provides a flow of air through the engine crankcase that is substantially directly proportional to engine speed.
In most multi-cylinder engines, the crankcase volume remains relatively constant as the pistons reciprocate. As one cylinder moves inward, and takes away crankcase volume, another piston is moving outward adding crankcase volume, so that the overall crankcase volume remains substantially constant. In single cylinder engines, and certain multi-cylinder configurations, however, the reciprocating motion of piston(s) causes a substantial cyclical variation in the crankcase volume for every rotation of the engine.
This invention recognizes that, in engines where the crankcase volume varies cyclically as the pistons reciprocate, the cyclical variation in crankcase volume can be utilized for providing positive crankcase ventilation. Utilizing the cyclical variation in crankcase volume, in accordance with the invention, provides a flow of air for positive crankcase ventilation that increases in direct proportion to engine speed, rather than undesirably decreasing in proportion to engine speed as was the case in prior PCV systems utilizing engine vacuum.